Difficulty with spiking after full fusing
- November 4, 2008 at 2:33 pm #9268
Hi! I am a beginner. I have fired twice with my new kiln. The first schedule included spikes so I tried a different one…. in the hopes that the schedule was the cause. I still had spiking. I am making pendants. They are nicely rounded and have no hazing. Out of a batch of about twenty pendants there is only one that has broken. The pre-fired pieces fit together well. Only a few of them had to be grinded. I have heard the problem might be the result of: overheating, firing too long, as well as fiber paper holding the piece too big. My fiber paper comes out flat after the firings. This is not the cause. Has anybody had spiking? If so, have you found what causes it? Is there a schedule you rely on that seems to eliminate it? If anybody would like to view my two schedules I can list them. Perhaps you will notice something that needs to be adjusted or eliminated. Maybe it is not the schedule, but something else in my fusing practice. ?
Thanks for your advice!November 4, 2008 at 7:23 pm #10959AnonymousInactiveNovember 5, 2008 at 3:38 pm #10960
Hi! What I mainly refer to as “spiking” are places that are sharp and often come to a point. Depending on the shape of the pendant some are more noticeable (ie.: a pendant that fires into a pear shape has a sharp elongated tip at its bottom…. maybe it might be more clearer if you think of a heart shape and where its rounded sides come together to a point). If you press very hard on these spikes you could cut yourself. I figure I might be able to use fine sandpaper that has been wettened and lightly rub on the pendants whose spikes are less sharp. I’ll have to be very careful to avoid any hazing. It’s worth a try. I looked over my pendants again, and I found most spikes usually occur at 90 degree angles. Several pieces without an obvious 90 degree angle tended to stretch and flatten at both ends. It looked as if the caps did not completely wrap around to the bases. Instead of being sharp these pendants were rough in the areas that did not completely cap over. There probably is a name for this type of problem. I thought I had cut the caps slightly bigger than the base and had them both shaped closely the same…. maybe I was slightly off. I prep my kiln by using kiln wash on the shelf. Before my first firing I also kiln washed my kiln. I place thick shelf paper on the shelf and posts underneath the shelf. With my first schedule my bases were rough. I was told this can happen. On my second schedule I swept out my kiln and tossed away the paper. The paper had almost turned to dust. I decided this time to turn over my paper and fire on the smoother side. This made a huge difference! The paper didn’t burn away and is reusable. I kept plenty of distance between each piece of fiber paper on the shelf. Each pendant was set on its own individual piece of shelf paper, and I laid at least an additional 1/2″ of paper around the pendant so as not to get glass on my shelf. All of the shelf paper laid completely flat. Here are my schedules:
THANKS SO MUCH!November 6, 2008 at 4:43 pm #10961katkramerParticipant
I experienced your “spiking” issue when I was first starting as well…
I went to the suggested firing schedules that Paul and Karen have posted on the site and was looking to compare…the main differences I noticed were they were going a little hotter on the full-fuse and holding for a little less time. I chose the single-layer fusing schedule since you’re doing jewelry components and they’re small, but the schedule is for larger pieces, and you could be a little less conservative on the ramp times and such.
Your 400° ramp is fine. On jewelry components I usually ramp a little faster, but 400° is safe.
I think the hold at 1250 for 60 minutes is unnecessary…the components are small. In Paul’s schedule, this allows the layers to squeeze bubbles out…60 is safe, and should minimize bubbles, but I usually don’t hold that long. Maybe 30 minutes at the most.
Now, your process temperature…I think this is where you’re having the problem. For a full-fuse, Paul has 1475° on the schedule, with a hold of 10 minutes. When I first started, I would use lower temperatures and hold longer…sometimes for up to 30-40 minutes, and I believe that this was causing my “spikes,” along with the use of the thicker, rougher fiber paper. Now I usually use the recommended process temperature, and hold for no more than 10 minutes. It varies by kiln, though, but not by much. I’ve had better results since I started going hotter and holding for a shorter time. I also used to open the kiln to “quick cool”, but I don’t do that anymore. I let it sit at the process temp for ten minutes, then let it ramp down to 960.
Anneal at 960 for about 30 minutes. Remember, jewelry components are small, and you won’t have as much of a problem with thermal shock.
And I will generally ramp down AFAP from 960 on jewelry components, although I’m much more conservative on larger pieces.
Paul may have other thoughts…but this works for me!November 8, 2008 at 2:50 pm #10962
Thanks so much for your advice! I tried a different schedule the other day. I have fused three different times with three different schedules. The schedule took forever to run! Also, I still had spiking! At least my carborundun tool (word and sp.?) works great for removing these awful things. I’ll try your schedule this next week. I’m anxious to see how things work out. I am confused on a couple of things. What ramp do you use to get up to your process temperature from the 1250? What do you consider the process temperature (Paul’s)? There’s a wide range. I figure you mean 1475. What ramp do you use after finishing your 960 hold? At what temperature do you let the kiln cool down naturally (ie.:750?)? I do apologize! I’m just a beginner with lots of questions…. Do you have a tack fuse schedule you like? If you do, would you mind sharing it? When I do master this full fuse I’ll be ready to move on. It seems with the schedules I’ve used for full I lose a lot of the detailing. I’m hoping with the correct full fuse schedule I won’t loose as much. I do realize a tack provides better detailing than a full.
Again, I appreciate your help! Enjoy your week-end! CindyNovember 10, 2008 at 8:43 pm #10963AnonymousInactive
The spikes you describe are caused by friction of the melted glass against the surface of the shelf. It is much more common when firing on fiber paper.
Fusing at a lower temperature – so that the glass is less liquid – will also help reduce the problem.
Helios Kiln Glass Studio
PaulTarlow.comNovember 14, 2008 at 3:11 pm #10964Donna SarafisParticipant
I have been working w/full fusing for the last six months when I start doing more than tack fusing most of my pieces. As I got over 1515 w/my larger kiln, I experienced really nice full fuses, but it began spiking w/certain colors that are softer. It was definitely just getting hotter that caused it, and you have to watch the colors. Some spike at lower temps.
DonnaNovember 21, 2008 at 12:35 am #10965katkramerParticipant
I find that Paul’s firing schedules are a little longer than I used to use, but my results have been SIGNIFICANTLY better. I wasted a couple of firings of other people’s stuff by ramping too fast…after that I vowed to find another way! I hate disappointing them after all their hard work. Also, a longer firing schedule doesn’t cost that much more…I think I figured an 18-hour schedule on my 24″x24″ kiln costs me about five bucks. But since you’re doing jewelry, your firings will be much shorter.
“Process” temperature is usually the highest temperature you go to…slumping, full fuse, tack fuse…whatever temperature you’re holding at to achieve that affect is your process temperature. The term is used on Bullseye’s technical documentation, so you’ll see it in other places!
Going up to the process temperature from 1250°, I usually go AFAP/9999. 1250° is a bubble squeeze, and the glass doesn’t shock when it’s that hot.
If I’m doing jewelry components, I either shut off the kiln after the 960° anneal and let it cool down, or use the AFAP (as fast as possible) ramp (9999 on my kiln). That confused me at first, because I thought it was “ramping” 9999° per hour UP, but if you’re final temperature on that segment is lower, it’s ramping DOWN.
Another difference from my earlier firings…I used to “flash cool” by lifting the lid of the kiln, but I understand it’s hard on the kiln. Paul and Karen suggested that I hold at the process temperature for 10 minutes or so, and this has worked fine. After 10 minutes, the kiln starts ramping down AFAP to 960, then holds to anneal. Of course kilns vary, but I’ve used this in both my 9″ AIM kiln and my 24″x24″ Jen Ken, and it works fine.
Paul also suggested firing on the paper-like shelf paper instead of fiber paper. With my larger items, I started putting fiber paper AND shelf paper underneath. I had problems with large bubbles, and this seems to have addressed the problem.
I noticed most of my problems occurred when I would hold at high temperatures, usually full fuse, for long periods of time.
Let us know how that works out for you!
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